Many people bridle at the idea that all the complex "inner" experiences they go through (thoughts, feelings, memories, etc.) could possibly be described as "just" chemical processes in their brains. These "chemical" processes could more correctly be described as electro-chemical, since they involve both the transmission of minute electrical currents (generated by chemical means) and the effects of other substances (chemicals) on the process.
Aside from those who refuse to accept that there is not a part of them that is eternal and immaterial, I think that this is mostly a matter of people not understanding how truly complicated the human brain is.
There are billions of neurons, or nerve cells in the human brain. Each one is also so much more than a "switch" (the idea of a switch relating to the individual components of a man made digital computing device). Each one is connected to many others, in ways that change as the brain lives. Each one has many subtle internal characteristics that also vary and change with growth. These functions are not only dependent on the internal characteristics of the neurons themselves, but also are affected, somtimes radically, by various substances as they course through the blood supply - from simple things like the blood sugar and oxygen levels to more complex effects due to hormones and other glandular secretions resulting from various stimuli. The subtlety of timing also plays a big part in the overall picture of what a given neuron "firing" means in terms of the subjective experience of the owner of the brain in question.
So combining the huge number of neurons with the many ways in which they can act and interact, there could easily be a trillion brain "states" for each arrangement of neuronal development - and these arrangements are constantly changing as we experience and learn.
There are about 30 million seconds in a year. A human life, lasting say, seventy years, comprises about 2 billion seconds. Just think about this for a moment... your brain is capable of registering probably a thousand times more conditions (thoughts, feelings, expereiences) at any given moment than there are seconds in your life! And each second or moment in your life constitutes a new arrangement with a huge number of possible states of consciousness...
I understand the typical reaction to the reductionist point of view that the brain is just a "bunch of chemicals" - but what a hugely complicated bunch of chemicals it is! It is far more complex than could be mapped and laid out in such a way that your every idea, wish, and dream could be defined and predicted, which I think is what some people don't like about this sort of description.
There is also the reaction against the seeming absence of "free will" in this scheme - to which I have two answers. One is that there are very few real opportunities in life to actually exercise truly free willing behaviour (most of our likes, dislikes and such that come into play when we "choose" are already programmed, uniquely of course, in our brain), and the other is something I have attempted to possibly explain elsewhere, as part of my theories about transcendental states.
© Huw Powell